The funeral of the poisoned Russian former spy Alexander Litvinenko was held today as it was claimed that a key witness in the murder inquiry had fallen into a coma.

The former spy was laid to rest this afternoon at Highgate Cemetery in north London.

Dmitry Kovtun

However, the burial service was overshadowed by an unscheduled interruption by an Islamic imam – specifically against the wishes of Mr Litvinenko’s widow.

The burial service was supposed to be a strictly non-denominational ceremony.

After Mr Litvinenko’s father had spoken at his graveside, an Islamic associate of his Chechen friend Ahmed Zakayev interrupted and performed a Muslim prayer.

Alex Goldfarb, one of the former spy’s closest friends, described it as an unfortunate detraction and said it was yet another thing Mr Litvinenko’s wife Marina had had to deal with.

It followed controversy over whether Mr Litvinenko had converted to Islam on his deathbed.

Mr Litvinenko’s father Walter said earlier this week that his son had requested before his death to be buried according to Muslim tradition.

However, his closest friends say they have “strong reservations” about this.

In another development tonight, it was disclosed that all seven staff who were working at the Pine Bar of the Millennium Hotel – where Mr Litvinenko had a meeting on the day he fell ill – had tested positive for low levels of radiation.

Prof Pat Troop, chief executive of the Health Protection Agency, said there were no short-term risks, but there was a “very small” increased long-term risk of cancer.

Following the results, the HPA will offer urine tests to more than 200 other people who were in the bar on that day, November 1, which is when Mr Litvinenko was first taken ill.

It was claimed tonight that the Russian businessman Dmitry Kovtun, who met the former spy on the day he was allegedly poisoned in London, was critically ill.

A Russian news agency claimed Mr Kovtun had fallen into a coma immediately after being questioned by Russian investigators and Scotland Yard detectives.